1. Field of the Invention
This invention relates to soaps suitable for skin and hair treatment and has particular reference to a novel antibacterial soap which comprises 2,4,4'-trichloro-2'-hydroxydiphenylether and one or more of an inorganic phosphorus oxyacid and a salt thereof.
2. Description of the Prior Art
2,4,4'-Trichloro-2'-hydroxydiphenylether is a known compound which possesses broad antibacterial spectrum characteristics for microorganisms such as Gram-positive and -negative bacteria, mold, yeast and the like. Moreover, the compound has lower toxic and irritating effects upon the skin and mucous membrane of human beings. Because of such substantial advantages, the compound is useful as a good antibacterial agent for inhibiting any noxious microorganisms which would adhere to the skin and hair, and therefore, can be expected to find wide application to soaps, shampoos, detergents, cosmetics, ointments and similar articles.
However, such antibacterial compound or 2,4,4'-trichloro-2'-hydroxydiphenylether is encountered with the drawback that the compound when incorporated into any conventional soap bases causes the resulting soaps to discolor or become dark brown when they are exposed to sunlight. Although discoloration in the soaps does not induce adverse effects upon the antibacterial action of the compound, nevertheless it mars attractive appearance of the soap product and makes the user feel uneasy. This problem is particularly detrimental to commercial acceptance of generally light-colored soaps. Accordingly, a need continues to exist for an antibacterial soap which produces no color deterioration even upon exposure to sunlight.
In fact, various attempts have been made to reduce, retard or prevent color formation in the soaps of the type described, and some reports on the problem have been made public. According to U.S. Pat. No. 3,284,362, an aromatic carboxylic acid or an alkali metal salt thereof is employed as a discolor-preventing agent in a soap composition. The use of a C.sub.8 -C.sub.22 substantially straight-chain fatty acid is disclosed in U.S. Pat. No. 3,625,903 and Japanese Pat. publication No. 47-20629. On the other hand, Japanese Pat. publication No. 52-43207 is concerned with the prevention of a soap from discoloration with the aid of an organic acid such as malonic acid, citric acid or malic acid. It has now been found that satisfactory results cannot still be obtained by such prior art techniques.
The present inventor has made many studies concerning minimizing or avoiding color formation or discoloration in a variety of antibacterial soaps into which 2,4,4'-trichloro-2'-hydroxydiphenylether is incorporated. As a result of those studies, it has been discovered that particular phosphoric oxyacids and salts thereof exhibit excellent discolor-preventing characteristics and are surprisingly efficient in keeping the soaps against discoloration. The present invention bases its achievement upon this discovery.